Blood thrombus, may embolize and form an embolus in a patient vasculature. Sometimes such emboli are harmlessly dissolved in the blood stream. At other times, however, such emboli may lodge in a blood vessel where they can partially or completely occlude the flow of blood. If the partially or completely occluded vessel feeds blood to sensitive tissue such as, the brain, lungs or heart, for example, serious tissue damage may result.
When symptoms of an occlusion are apparent, such as an occlusion resulting in a stroke, immediate action should be taken to reduce or eliminate resultant tissue damage. One approach is to treat a patient with clot dissolving drugs. These drugs, however, do not immediately dissolve the clot from the patient.
Embolectomy cages are used to treat strokes where blood flow in a vessel is blocked by an embolus. These devices function to remove the embolus and recanulate the vessel lumen by compressing the embolus into the lumen wall, macerating the embolus by pulling the device through the embolus, capturing the embolus by pulling the embolus into the interior of the device, breaking the embolus into smaller pieces to facilitate aspiration, anchoring the embolus so that it does not migrate distally during aspiration, and combinations thereof.
Prior art devices, such as those disclosed in U.S. Patent Publication Nos. 2002/0058904 and 2007/0208367, incorporated herein by reference in their entireties, create a radial force that tears through the embolus as the device expands, after which the embolus penetrates into the interior of the device to be captured in a dense net at the distal end of the device. In such devices, relatively high pressure needed to sever the fibrin networks of the blood clot forming the embolus. Other prior art devices tear the embolus from the wall of the vessel using a shear force, wherein an axial force is applied to the device in addition to radial forces to tear the embolus from the wall of the vessel.
Typical embolectomy cages have openings with areas in the range of about 5×107 μm2 to about 3×105 μm2. Struts forming the embolectomy cages are about 100 μm to about 40 μm wide. Smaller openings in embolectomy cages result in more struts, which, in turn, distribute the total radial force required to engage an embolus over a larger portion of the wall of the vessel. However, emboli do not engage well with smaller openings, due to an inability to penetrate the smaller openings.
Larger openings in embolectomy cages allow for better engagement of the embolus by the embolectomy cage, such as described in co-pending and co-owned U.S. Patent Publication No. 2012/0123466, incorporated herein by reference in its entirety. However, such larger openings reduce the number of struts, resulting in the total radial force required to engage the embolus being distributed over fewer struts. Because strut widths are typically within the above-listed range, this arrangement increases the local pressure that each strut places on the vessel wall, which could lead to vascular damage. Using wider struts to distribute the force over a greater area creates a device with greater bending stiffness.